18 GEOLOGY OF THE EUEEKA DISTIUCT. 



Silverado block on the one side and the depressed Spring Hill and Carljon 

 Ridge block on the other. On the west side, wherever the volcanic and 

 detrital material fails to conceal the underlying rocks only Carboniferous 

 sti'ata are exposed, whereas, on the opposite side Silurian strata every- 

 where rise above the fault line in bold and abi-upt ridges. 



Starting from the southern end of the mountains the fault follows u]) 

 Pinto Valley, with Carbon Ridge on the west and English Mountain on the 

 east, the intermediate valley being filled with jnimices and tuffs. Not 

 until nearly opposite Dome Mountain do the sedimentary beds on both 

 sides of the fault come in direct contact at the surface, but here we find 

 the Lower Coal-measures limestone brought up unconformably against the 

 Lone Mountain limestone. From here a deep, narrow limestone gorge 

 extends northward, along which the limestones of the two different 

 epochs stand out boldly on ojjposite walls, the direction of the gorge coin- 

 ciding with the line of the fault. Where the drainage channel following 

 the gorge turns abruptly toward the west the Eureka quartzite comes in 

 beneath the Lone Mountain strata, but the fault, without deviating in the 

 least from its course, continues northward with the Carboniferous limestone 

 still on the west side. A short distance farther northward the sedimentary 

 strata are buried beneath the lavas of Richmond Mountain. The vertical dis- 

 placement along the Pinto is probably quite as great as that found along 

 the Hoosac fault; the same geological horizons are here brought into juxta- 

 position, although higher beds form the contact along the Pinto fault, and 

 at Carbon Ridge the Weber conglomerates come in as the uppermost beds. 

 The enormous development of Devonian strata and the Diamond Peak 

 quartzite, which, as shown by the section, have an estimated thickness of 

 11,000 feet, is wholly wanting. 



Rescue Fault.— About 2f miles east of the Pinto fault, and on the east side 

 of the Silverado and County Peak block, runs the equally persistent but 

 less profound Rescue fault. It derives its name from Rescue Canyon, 

 which, in turn, owes its origin primarily to the fiiult. The canyon, a longi- 

 tudinal mountain valley nearly 2 miles in length, opening out into Fish 

 Creek Basin, is now occupied for the entire distance by rhyolite extrava- 

 sated along the course of the fault. At the head of tlie canyon the rhvolite 



